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• 301.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. Bell Laboratories, Alcatel-Lucent Murray Hill, NJ 07974, USA.
Aspects of Favorable Propagation in Massive MIMO2014Ingår i: European Signal Processing Conference (EUSIPCO), EURASIP , 2014, s. 76-80Konferensbidrag (Refereegranskat)

Favorable propagation, dened as mutual orthogonality among the vector-valued channels to the terminals, is one of the key properties of the radio channel that is exploited in Massive MIMO. However, there has been little work that studies this topic in detail. In this paper, we first show that favorable propagation offers the most desirable scenario in terms of maximizing the sum-capacity. One useful proxy for whether propagation is favorable or not is the channel condition number. However, this proxy is not good for the case where the norms of the channel vectors are not equal. For this case, to evaluate how favorable the propagation oered by the channel is, we propose a distance from favorable propagation measure, which is the gap between the sum-capacity and the maximum capacity obtained under favorable propagation. Secondly, we examine how favorable the channels can be for two extreme scenarios: i.i.d. Rayleigh fading and uniform random line-of-sight(UR-LoS). Both environments offer (nearly) favorable propagation. Furthermore, to analyze the UR-LoS model, we propose an urns-and-balls model. This model is simple and explains the singular value spread characteristic of the UR-LoS model well.

• 302.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. Bell Laboratories, Alcatel-Lucent, NJ, USA.
Energy and Spectral Efﬁciency of Very Large Multiuser MIMO Systems2013Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, nr 4, s. 1436-1449Artikel i tidskrift (Refereegranskat)

A multiplicity of autonomous terminals simultaneously transmits data streams to a compact array of antennas. The array uses imperfect channel-state information derived from transmitted pilots to extract the individual data streams. The power radiated by the terminals can be made inversely proportional to the square-root of the number of base station antennas with no reduction in performance. In contrast if perfect channel-state information were available the power could be made inversely proportional to the number of antennas. Lower capacity bounds for maximum-ratio combining (MRC), zero-forcing (ZF) and minimum mean-square error (MMSE) detection are derived. An MRC receiver normally performs worse than ZF and MMSE. However as power levels are reduced, the cross-talk introduced by the inferior maximum-ratio receiver eventually falls below the noise level and this simple receiver becomes a viable option. The tradeoff between the energy efficiency (as measured in bits/J) and spectral efficiency (as measured in bits/channel use/terminal) is quantified for a channel model that includes small-scale fading but not large-scale fading. It is shown that the use of moderately large antenna arrays can improve the spectral and energy efficiency with orders of magnitude compared to a single-antenna system.

• 303.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. Bell Laboratories, Alcatel-Lucent, Murray Hill, NJ 07974, USA.
Massive MU-MIMO Downlink TDD Systems with Linear Precodingand Downlink Pilots2013Ingår i: 51st Annual Allerton Conference on Communication, Control, and Computing (Allerton), 2013, IEEE , 2013, s. 293-298Konferensbidrag (Refereegranskat)

We consider a massive MU-MIMO downlink time-division duplex system where a base station (BS) equipped with many antennas serves several single-antenna users in the same time-frequency resource. We assume that the BS uses linear precoding for the transmission. To reliably decode the signals transmitted from the BS, each user should have an estimate of its channel. In this work, we consider an efficient channel estimation scheme to acquire CSI at each user, called beamforming training scheme. With the beamforming training scheme, the BS precodes the pilot sequences and forwards to all users. Then, based on the received pilots, each user uses minimum mean-square error channel estimation to estimate the effective channel gains. The channel estimation overhead of this scheme does not depend on the number of BS antennas, and is only proportional to the number of users. We then derive a lower bound on the capacity for maximum-ratio transmission and zero-forcing precoding techniques which enables us to evaluate the spectral efficiency taking into account the spectral eciency loss associated with the transmission of the downlink pilots. Comparing with previous work where each user uses only the statistical channel properties to decode the transmitted signals, we see that the proposed beamforming training scheme is preferable for moderate and low-mobility environments.

• 304.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. Bell Laboratories, Alcatel-Lucent, NJ, USA .
The Multicell Multiuser MIMO Uplink with Very Large Antenna Arrays and a Finite-Dimensional Channel2013Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 61, nr 6, s. 2350-2361Artikel i tidskrift (Refereegranskat)

We consider multicell multiuser MIMO systems with a very large number of antennas at the base station (BS). We assume that the channel is estimated by using uplink training. We further consider a physical channel model where the angular domain is separated into a ﬁnite number of distinct directions. We analyze the so-called pilot contamination effect discovered in previous work, and show that this effect persists under the ﬁnite-dimensional channel model that we consider. In particular, we consider a uniform array at the BS. For this scenario, we show that when the number of BS antennas goes to inﬁnity, the system performance under a ﬁnite-dimensional channel model with P angular bins is the same as the performance under an uncorrelated channel model with P antennas. We further derive a lower bound on the achievable rate of uplink data transmission with a linear detector at theBS. We then specialize this lower bound to the cases of maximum-ratio combining (MRC) and zero-forcing (ZF) receivers, for a ﬁnite and an inﬁnite number of BS antennas. Numerical results corroborate our analysis and show a comparison between the performances of MRC and ZF in terms of sum-rate.

• 305.
Chalmers University of Technology, Gothenburg, Sweden. Blekinge Institute of Technology, Karlskrona, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Uplink Performance Analysis of Multicell MU-SIMO Systems with ZF Receivers2013Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359Artikel i tidskrift (Refereegranskat)

We consider the uplink of a multicell multiuser single-input multiple-output system where the channel experiences both small and large-scale fading. The data detection is done by using the linear zero-forcing technique, assuming the base station (BS) has perfect channel state information of all users in its cell. We derive  new, exact analytical expressions for the uplink rate, symbol error rate, and outage probability per user, as well as alower bound on the achievable rate. This bound is very tight and becomes exact in the large-number-of-antennas limit. We further study the asymptotic system performance in the regimes of high signal-to-noise ratio (SNR), large number of antennas, and large number of users per cell. We show that at high SNRs, the system is interference-limited and hence, we cannot improve the system performance by increasing the transmit power of each user. Instead, by increasing the number of BS antennas, the effects of interference and noise can be reduced, thereby improving the system performance. We demonstrate that, with very large antenna arrays at the BS, the transmit power of each user can be made inversely proportional to the number of BS antennas while maintaining a desired quality-of-service. Numerical results are presented to verify our analysis.

• 306.
Queen's University Belfast, Belfast, BT3 9DT, U.K.. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Massive MIMO with Optimal Power and Training Duration Allocation2014Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 3, nr 6, s. 605-608Artikel i tidskrift (Refereegranskat)

We consider the uplink of massive multicell multiple-input multiple-output systems, where the base stations (BSs), equipped with massive arrays, serve simultaneously several terminals in the same frequency band. We assume that the BS estimates the channel from uplink training, and then uses the maximum ratio combining technique to detect the signals transmitted from all terminals in its own cell. We propose an optimal resource allocation scheme which jointly selects the training duration,training signal power, and data signal power in order to maximize the sum spectral efficiency, for a given total energy budget spent in a coherence interval. Numerical results verify the benets of the optimal resource allocation scheme. Furthermore, we show that more training signal power should be used at low signal-to-noise ratio(SNRs), and vice versa at high SNRs. Interestingly, for the entire SNR regime, the optimal training duration is equal to the number of terminals.

• 307.
Department of Signals and Systems, Chalmers University of Technology, Gothenburg, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Performance Analysis of Large Scale MU-MIMO with Optimal Linear Receiver2012Ingår i: Proceedings of the IEEE Swedish Communication Technologies Workshop (Swe-CTW), IEEE , 2012, s. 59-64Konferensbidrag (Refereegranskat)

We consider the uplink of multicell multiuser MIMO(MU-MIMO) systems with very large antenna arrays at the base station (BS). We assume that the BS estimates the channel through uplink training, and then uses this channel estimate to detect the signals transmitted from a multiplicity of autonomous users in its cell. By taking the correlation between the channel estimate and the interference from other cells into account, we propose an optimal linear receiver (OLR) which maximizes the received signal-to-interference-plus-noise (SINR). Analytical approximations of the exact and lower bound on the achievable rate are then derived. The bound is very tight, especially at large number of BS antennas. We show that at low SINR, maximal-ratio combing (MRC) receiver performs as well as OLR, however at high SINR, OLR outperforms MRC. Compared with the typical minimum mean-square error receiver, our proposed OLR improves systematically the system performance, especially when the interference is large.

• 308.
University of Peradeniya, Peradeniya 20400, Sri Lanka . Queen's University Belfast, Belfast, BT3 9DT, U.K.. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Multipair Full-Duplex Relaying with Massive Arrays and Linear Processing2014Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 32, nr 9, s. 1721-1737Artikel i tidskrift (Refereegranskat)

We consider a multipair decode-and-forward relay channel, where multiple sources transmit simultaneously their signals to multiple destinations with the help of a full-duplex relay station. We assume that the relay station is equipped with massive arrays, while all sources and destinations have a single antenna. The relay station uses channel estimates obtained from received pilots and zero-forcing (ZF) or maximum-ratio combining/maximum-ratio transmission (MRC/MRT) to process the signals. To signicantly reduce the loop interference effect, we propose two techniques: i) using a massive receive antenna array; or ii) using a massive transmit antenna array together with very low transmit power at the relay station. We derive an exact achievable rate expression in closed-form for MRC/MRT processing and an analytical approximation of the achievable rate for ZF processing. This approximation is very tight, particularly for a large number of relay station antennas. These closed-form expressions enable us to determine the regions where the full-duplex mode outperforms the half-duplex mode, as well as to design an optimal power allocation scheme. This optimal power allocation scheme aims to maximize the energy efficiency for a given sum spectral efficiency and under peak power constraints at the relay station and sources. Numerical results verify the effectiveness of the optimal power allocation scheme. Furthermore, we show that, by doubling the number of transmit/receive antennas at the relay station, the transmit power of each source and of the relay station can be reduced by 1.5 dB if the pilot power is equal to the signal power, and by 3 dB if the pilot power is kept fixed, while maintaining a given quality of service.

• 309.
Live Demonstration of Mismatch Compensation for Time-Interleaved ADCs2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

The purpose of this thesis is to demonstrate the effects of mismatch errors that occur in time-interleaved analog-to-digital converters (TI-ADC) and how these are compensated for by proprietary methods from Signal Processing Devices Sweden AB. This will be demonstrated by two different implementations, both based on the combined digitizer/generator SDR14. These demonstrations shall be done in a way that is easy to grasp for people with limited knowledge in signal processing.

The first implementation is an analog video demo where an analog video signal is sampled by such an TI-ADC in the SDR14, and then converted back to analog and displayed with the help of a TV tuner. The mismatch compensation can be turned on and off and the difference on the resulting video image is clearly visible.

The second implementation is a digital communication demo based on W-CDMA, implemented on the FPGA of the SDR14. Four parallel W-CDMA signals of 5 MHz are sent and received by the SDR14. QPSK, 16-QAM, and 64-QAM modulated signals were successfully sent and the mismatch effects were clearly visible in the constellation diagrams. Techniques used are, for example: root-raised cosine pulse shaping, RF modulation, carrier recovery, and timing recovery.

• 310.
Department of Information and Communication Systems Engineering, University of the Aegean, Samos, Greece.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. Department of Electrical Engineering and Automation, School of Electrical Engineering, Aalto University, Espoo, Finland. ABB Corporate Research, Paden, Switzerland.
Deadline-constrained Bursty Traffic in Random Access Wireless Networks2018Ingår i: 2018 IEEE 19th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), IEEE, 2018Konferensbidrag (Refereegranskat)

We consider a network of buffer-aided wireless devices having to transmit deadline-constrained data packets on a slotted-ALOHA random-access channel. While retransmission- based communication enhances reliability, the transmission of packets in the queue is delayed and as a result, they might get dropped before they are transmitted successfully. In this work, we study the performance of deadline-constrained bursty traffic with retransmissions providing a Markov chain-based analysis. The aim is to reveal the trade-off between the packet deadline and the number of retransmissions as a function of the arrival rate, and pave the way towards finding the optimal number of retransmissions, given the packet deadline and packet arrival rate. Furthermore, performance evaluation is conducted for a user with varying transmit probability and different number of retransmissions. The results reveal the effect of these parameters on the drop probability and average throughput showing the values under which, improved performance can be obtained.

• 311.
Double Differential TOA Positioning for GSM2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

For most time-based positioning techniques, synchronization between the objectsin the system is of great importance. GPS (global positioning system) signalshave been found very useful in this area. However, there are some shortcomingsof these satellite signals, making the system vulnerable. The aim of this masterthesis is to investigate an alternative method for synchronization, independent ofGPS signals, which could be used as a complement. The proposed method takesadvantage of the broadcast signals from telecommunication towers, and use themfor calculation of the synchronization error between two receivers. By looking atthe time difference between arrival times at the receivers, and compare it to thetrue time difference, the synchronization error can be found. A precondition isthat the locations of the receivers as well as the tele tower are known beforehand,so that the true time difference can be calculated using geometry.The arrival times are determined through correlation between the received signalsand known training bits, which are a part of the transmission sequence. Forverification, experiments were made on localization of a mobile phone in theGSM (global system of mobile communications) network.This researchwas a collaboration with FOI, the Swedish Defense Research Agency,where most of the work was done.

• 312.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
Is the Cyclic Prefix Needed in Massive MIMO?2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Massive multiple-input-multiple-output (MIMO) is a wireless communication technologythat usesa large number of antennas at the base station and servesmultiple terminals over the same time-frequency resource.This technique can achievehigher data rates than existing communication technology, which only serves one terminal per resource. That is why Massive MIMO is considered a promising candidate for 5G. Orthogonal frequency division multiplexing (OFDM) can be used for transmitting information at different sub-channels. The cyclic prefix (CP) is a repetition of the last samples in a symbol, which is appended at the beginning of the symbol.It serves as a guard interval between consecutive symbols to avoid inter-symbol interference (ISI) and to make sub-channels orthogonal. In this thesis it is proposed to shorten the CP length in Massive MIMO. The shortening of the CP length will increase the effective spectral efficiency but also create additional interference. This trade-off is investigated. A simulation based study is performed to analyse the effective achievable rate of anuplink Massive MIMO system in a single-cell scenario when 10000 Gaussian symbols are transmitted.In the simulation, the number of sub-channels is 128. They are transmitted through a channel with 10 taps. With the classical CP length9samples and a massive MIMO base stationwith 50 antennas serving 3 terminals,the effective achievable rate was 3.863 bits/s/Hz. It was found thatthe effective achievable rate is maximized when the CP length is shortened to 6 samples; the effective achievable rate then became 4.112 bits/s/Hz.In the same system when 100 antennas are used, the corresponding effective achievable rates are 4.791 bits/s/Hz and 4.895 bits/s/Hz with an optimum CP lengthof5 samples. It is shown that the optimum CP length in Massive MIMO is not equal to the number of taps minus one which is the conventional choice. Yes, the CP is needed in Massive MIMO, but it can be shorter than conventionally.

• 313.
High Speed IO using Xilinx Aurora2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

A VHDL evaluation platform and interface to the Xilinx Aurora 8b/10b IP has been designed, tested and evaluated. The evaluation platform takes an arbitrary amount of data sources and sends the data over 1,2,4 or 8 multi gigabit serial lanes, using the Aurora 8b/10b protocol. A lightweight communications protocol for point-to-point data transfer, error detection and recovery is used to maintain a reliable and efficient transmission scheme. Priority between sources sharing the serial link is also a part of the platform. The Aurora 8b/10b IP is a lightweight protocol and transceiver interface for Xilinx FPGAs, based on the 8b/10b line encoding protocol. In addition, a demonstration PCB has been developed to introduce the Kintex-7 FPGA to future products at SAAB Dynamics.

• 314.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
Enhancements in LTE OTDOA Positioning for Multipath Environments2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

By using existing radio network infrastructure, a user can be positioned even where GPS and other positioning technologies lack coverage. The LTE Positioning Protocol (LPP) supports user Reference Signal Time Difference (RSTD) reports based on the Time of Arrival (TOA) for a Positioning Reference Signal (PRS). In the current reporting format, only one RSTD for each base station is considered, but for indoor environments this is easily biased due to fading and multipath issues, resulting in a Non-Line of Sight (NLOS) bias. With a rich User Equipment (UE) feedback that can represent the multipath channel for each Base Station (BS), the positioning accuracy can be increased. This thesis develops and evaluates a UE reporting format representing multiple TDOA candidates, and a probabilistic positioning algorithm, in terms of positioning accuracy and amount of data reported. By modeling time measurements as Gaussian Mixture (GM), the time information can be compressed with arbitrary resolution and used in a Maximum-Likelihood (ML) estimation to find the position. Results were obtained through simulation in a radio network simulator and post-processing of simulation data in Matlab. The results suggest that several TOA candidates improve the positioning accuracy, but that the largest improvement comes from a noise based threshold by increasing LOS detectability reducing the NLOS bias, while suppressing noise. The results also suggest that the accuracy for the method can be further improved by combining multiple time measurement occasions.

• 315.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
Network-Based Positioning Using Last Visited Cells Report2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

The positioning performance with the LVC (Last Visited Cells) report is evaluated and compared with extended reports with signal strength data. The LVC report contains cell identities and time spent in the last cells listened to. This is an off-line data source and the purpose of the positioning is to extract information about users’ whereabouts, which for example can be used to optimize the cellular network or vehicular traffic. The positioning evaluation is done in Matlab with a log-distance model, a fingerprinting algorithm, and a new LVC specific algorithm. A particle filter and a particle smoother is used to process simulated LVC reports and extended reports with different amount of information. The results are compared and evaluated with regard to the positioning accuracy and the information density of the reports.

• 316.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
5G Simulation Framework2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

From the first generation, 1G, to the fourth generation, 4G, the development and technological advancements in telecommunications network systems have been remarkable. Faster and better connections have opened up for new markets, ideas and possibilities, to that extent that there now is a demand that surpasses the supply. Despite all these advancements made in the mobile communications field most of the concept of how the technology works and its infrastructure has remained the same. This however, is about to change with the introduction of the fifth generation (5G) mobile communication.

With the introduction of 5G much of the technology introduced will be different from that of previous generations. This change extends to include the entire infrastructure of the mobile communications system. With these major changes, many of the tools available today for telecommunications network evaluation do not really suffice to include the 5G network standard. For this reason, there is a need to develop a new kind of tool that will be able to include the changes brought by this new network standard.

In this thesis a simulation framework adapted for the next generation telecommunication standard 5G is set to be developed. This framework should include many of the characteristics that set 5G aside from previous generations.

• 317.
Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India. Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India. Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
Boru̇vka-incremental power greedy heuristic for strong minimum energy topology in wireless sensor networks2015Ingår i: Proceeding ICDCN '15 Proceedings of the 2015 International Conference on Distributed Computing and Networking, Association for Computing Machinery , 2015, artikel-id 25Konferensbidrag (Refereegranskat)

Given a set of sensors, the strong minimum energy topology (SMET) problem is to assign transmission range to each sensor node so that the sum of the transmission range for all the sensor is minimum subject to the constraint that the network is strongly connected (there is a directed path between every pair of nodes in the Network). This problem is known to be NP-hard. As this problem has lots of practical applications, several approximation algorithms and heuristics have been proposed. In this paper, we propose a new heuristic called Boru̇vka-incremental power greedy heuristic based on the Boru̇vka algorithm for the minimum spanning tree (MST) problem for solving the SMET problem. We compare the performance of the Boru̇vka-incremental power greedy heuristic with Kruskal-incremental power greedy heuristic and Prim-incremental power greedy heuristic. Extensive simulation results illustrate that Boru̇vka heuristic outperforms the Kruskal-incremental power greedy heuristic and Prim-incremental power greedy heuristic. We have also proved that apart from providing significant improvement in terms of average power savings, Boru̇vka incremental power greedy heuristic takes O(n) time for planar graphs as compared to O(n log n) time taken by Kruskal-incremental power greedy heuristic and O(n2) time taken by Prim-incremental power greedy heuristic, where n is the number of nodes in the network.

• 318.
Computer Science and Application Group, Department of Mathematic, IIT Delhi, New Delhi 110016, India.
Computer Science and Application Group, Department of Mathematic, IIT Delhi, New Delhi 110016, India. Department of Electrical Engineering, IIT Delhi, New Delhi 110016, India. Department of Electrical Engineering, IIT Delhi, New Delhi 110016, India.
New heuristics for strong minimum energy topology with reduced time complexity2018Ingår i: 2017 IEEE International Conference on Advanced Networks and Telecommunications Systems (ANTS), Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 1-6Konferensbidrag (Refereegranskat)

The strong minimum energy topology (SMET) problem is to assign transmission range to a set of sensors, such that the resulting topology is strongly connected and the sum of transmit powers of all the sensors is minimized. This problem, having wide range of applications, is known to be NP-hard and also APX-hard for 3-dimension space. Several heuristics and approximation algorithms have been proposed for this problem. In this paper, we first present an enhanced version of Prim-incremental power greedy heuristic which improves the running time of the existing algorithm by a factor of n, i.e., from O(n3) to O(n2), where n is the number of nodes in the network. Simulations results are also presented to support the theoretical result. Next we propose a new heuristics for SMET problem called Hybrid heuristic, which is based on BorÛvka and Prim MST algorithms and is shown to have lower complexity than both of them. Lastly, we show that this Hybrid heuristics which can provide energy efficiency gains over the existing ones is also the fastest power greedy heuristics for SMET problem when the nodes and links of the network form a planar graph.

• 319.
ICube Laboratory, University of Strasbourg, France.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. ICube Laboratory, University of Strasbourg, France. ICube Laboratory, University of Strasbourg, France. Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
Distributed adaptive scheme for reliable data collection in fault tolerant WSNs2015Ingår i: Internet of Things (WF-IoT), 2015 IEEE 2nd World Forum on, Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 116-121Konferensbidrag (Refereegranskat)

Reliable data packet transfer is an essential facet of quality of service in Wireless Sensor Networks (WSNs). WSNs require pertinent and reliable data collection schemes to provide dependable information. We analyze the factors that affect reliability, and design efficient combinations of the possible options. While many researchers have tackled this issue by focusing on particular layers of the embedded communication stack (e.g., Medium Access Control (MAC) or routing layer), we propose a layer-independent transmission rate adaptive scheme, where no additional control messages are required. We focus on packet loss avoidance along prone-to-failure paths to the sink with the main objective being the efficient queue management of a sensor node. Based on certain factors (e.g., application or queue requirements) nodes will consequently take adjustment decisions. Our thorough simulation experiments demonstrate that DRAS reduces the packet drops and improves the data collection procedure in an energy efficient manner.

• 320.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
Performance Analysis of a System with Bursty Traffic and Adjustable Transmission Times2018Ingår i: 15th International Symposium on Wireless Communication System (ISWCS 2018): SS5 - Ultra-Reliable Low Latency Communications, IEEE Communications Society, 2018, s. 1-6Konferensbidrag (Refereegranskat)

In this work, we consider the case where a source with bursty traffic can adjust the transmission duration in order to increase the reliability. The source is equipped with a queue in order to store the arriving packets. We model the system with a discrete time Markov Chain, and we characterize the performance in terms of service probability and average delay per packet. The accuracy of the theoretical results is validated through simulations. This work serves as an initial step in order to provide a framework for systems with arbitrary arrivals and variable transmission durations and it can be utilized for the derivation of the delay distribution and the delay violation probability.

• 321.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten. University of Patras, Greece.
Throughput and Delay Analysis of Wireless Caching Helper Systems with Random Availability2018Ingår i: IEEE Access, E-ISSN 2169-3536, Vol. 6, s. 9667-9678Artikel i tidskrift (Refereegranskat)

In this paper, we investigate the effect of bursty traffic and random availability of caching helpers in a wireless caching system. More explicitly, we consider a general system consisting of a caching helper with its dedicated user in proximity and another non-dedicated user requesting for content. Both the non-dedicated user and the helper have limited storage capabilities. When the user is not able to locate the requested content in its own cache, then its request shall be served either by the caching helper or by a large data center. Assuming bursty request arrivals at the caching helper from its dedicated destination, its availability to serve other users is affected by the request rate, which will further affect the system throughput and the delay experienced by the non-dedicated user. We characterize the maximum weighted throughput and the average delay per packet of the considered system, taking into account the request arrival rate of the caching helper, the request probability of the user and the availability of the data center. Our results provide fundamental insights in the throughput and delay behavior of such systems, which are essential for further investigation in larger topologies.

• 322.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
University of Patras, Greece. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
Network-level Cooperation in Random Access IoT Networks with Aggregators2018Ingår i: International Teletraffic Congress (ITC 30), 2018Konferensbidrag (Refereegranskat)

In this work, we consider a random access IoT wireless network assisted by two aggregators. The nodes and the aggregators are transmitting in a random access manner under slotted time, the aggregators use network-level cooperation. We assume that all the nodes are sharing the same wireless channel to transmit their data to a common destination. The aggregators with out-of-band full duplex capability, are equipped with queues to store data packets that are transmitted by the network nodes and relaying them to the destination node. We characterize the throughput performance of the IoT network. In addition, we obtain the stability conditions for the queues at the aggregators and the average delay of the packets.

• 323.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
Pursuing the Potential of New Mechanisms for Performance Engineering of 5G2017Ingår i: 2017 IEEE 22ND INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD), IEEE , 2017Konferensbidrag (Refereegranskat)

In this position paper, we provide a discussion of the need for new mechanisms towards optimizing the performance of the firth generation (5G) wireless systems, and then we outline on-going research work and results in this direction. Initially we go over the recently proposed concept of network anticipation and then resource allocation, since these two themes form the core of the ACT5G research project. Then, we discuss two specific topics within the project. The first is the use of stochastic modeling for millimeter wave (mmWave) systems, which are expected to be part of 5G networks. Our modeling enables network anticipation, resulting in an estimation of the coverage probability of mmWave, including coverage with non-line-of-sight (NLOS) mmWave beams. In the second research topic, we address the use of scalable and dynamic transmission time interval (TTI) for scenarios with a mix of different traffic types. In addition, and highlight the importance of optimizing the channel and TTI allocation in this context. Numerical results of these studies are presented and discussed. Finally, we outline directions for future study.

• 324.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
Intel Corporation, Santa Clara, USA. Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten. Computer Science Department, University of Crete. Department of Electrical and Computer Engi- neering and Institute for Systems Research, University of Maryland, College Park, MD 20742..
Wireless Network-Level Partial Relay Cooperation: A Stable Throughput Analysis2018Ingår i: Journal of Communications and Networks, ISSN 1229-2370, E-ISSN 1976-5541, Vol. 20, nr 1, s. 93-101Artikel i tidskrift (Refereegranskat)

In this work, we study the benefit of partial relay cooperation. We consider a two-node system consisting of one source and one relay node transmitting information to a common destination. The source and the relay have external traffic and in addition, the relay is equipped with a flow controller to regulate the incoming traffic from the source node. The cooperation is performed at the network level. A collision channel with erasures is considered. We provide an exact characterization of the stability region of the system and we also prove that the system with partial cooperation is always better or at least equal to the system without the flow controller.

• 325.
Department of Telecommunications, Supelec Gif-sur-Yvette, France.
Department of Telecommunications, Supelec Gif-sur-Yvette, France.
Performance analysis of distributed cooperation under uncoordinated network interference2014Ingår i: 2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2014, s. 6181-6185Konferensbidrag (Refereegranskat)

Managing interference is a major technical challenge in large wireless networks. Distributed cooperation techniques, such as Interference Alignment (IA), exploit the available spatial degrees of freedom of the interference channel holding promise of enhanced spectral efficiency. Most prior results, however, consider isolated network settings, neglecting the interference from nodes that are not participating in the cooperation scheme. This paper analyzes the performance of IA in the presence of uncoordinated interference from a heterogeneous network. Specifically, we analyze perfect downlink IA in a fixed-size cell, where the interfering nodes are distributed according to a spatial point process, and compare it with a non-cooperative MIMO scheme. Furthermore, the performance gains by using a guard zone between the IA cluster and the interference field are evaluated and design guidelines for the necessary isolation distance from out-of-cluster interferers are provided.

• 326.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
Supélec, Department of Telecommunications, Gif-sur-Yvette, France.
Throughput of a Cognitive Radio Network under Congestion Constraints: A Network-Level Study2014Ingår i: 2014 9TH INTERNATIONAL CONFERENCE ON COGNITIVE RADIO ORIENTED WIRELESS NETWORKS AND COMMUNICATIONS (CROWNCOM), IEEE , 2014, s. 162-166Konferensbidrag (Refereegranskat)

In this paper we analyze a cognitive radio network with one primary and one secondary transmitter, in which the primary transmitter has bursty arrivals while the secondary node is assumed to be saturated (i.e. always has a packet waiting to be transmitted). The secondary node transmits in a cognitive way such that it does not impede the performance of the primary node. We assume that the receivers have multipacket reception (MPR) capabilities and that the secondary node can take advantage of the MPR capability by transmitting simultaneously with the primary under certain conditions. We obtain analytical expressions for the stationary distribution of the primary node queue and we also provide conditions for its stability. Finally, we provide expressions for the aggregate throughput of the network as well as for the throughput at the secondary node.

• 327.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem.
Self-Organized TDMA protocol for Tactical Data Links2011Självständigt arbete på avancerad nivå (masterexamen), 30 poäng / 45 hpStudentuppsats (Examensarbete)

A Tactical Data Link (TDL) system has been deployed in many military missions as a winning strategy. The performance of a TDL system is governed by the MAC protocol. The MAC protocol that is able to provide more flexibility and high quality of services is more desirable. However, most MAC protocols implemented in current TDL systems are based on a preprogramming TDMA protocol, in which a time slot schedule is fixed. This thesis presents the new self-organized TDMA protocol based on the existing self-organized slot assignment algorithms and the practical military scenarios as the alternative solution to the current preprogramming TDMA protocol. The self-organized TDMA protocol presented in this thesis is based on the Node Activation Polling Access (NAPA), Virtual Slot (VSLOT), and message based slot assignment algorithms. To evaluate the performance of the designed self-organized TDMA protocol over the preprogramming TDMA protocol, the simulation models for both protocols were implemented and simulated with NS-2 under the specific study scenarios. The results show that the self-organized TDMA protocol offers more flexibility and higher performance than the preprogramming TDMA protocol. In addition, the aspects of stability and security for the self-organized TDMA protocol were discussed. The overall conclusion is that the self-organized TDMA protocol could be a viable alternative for a future TDL system.

• 328.
Linköpings universitet, Institutionen för beteendevetenskap och lärande, Avdelningen för pedagogik och didaktik i utbildning och skola (PeDiUS).
Forskning om informations- och kommunikationsteknik: en översikt över verksamhet inom Norden2000Rapport (Övrigt vetenskapligt)
• 329.
Range Based Indoor Localization in Wireless Sensor Networks with Telos2013Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Localization of individual nodes in a wireless network is useful in many applications, e.g for tracking patients in hospitals. Using the Received Signal Strength Indicator, RSSI, for this purpose has been explored in numerous studies. It is energy efficient and rarely requires customised hardware of configuration. The possibility to use pre-configured, off-the-shelf products is especially important in large scale sensor network deployments. Using RSSI has, however, many drawbacks, since the radio signal is heavily affected by the surrounding envi- ronment. Most studies in this area discuss the impact of multipath effects. Our study on range based distance estimations, using the Telos hardware, shows that individual profiling requirements and antenna quality are equally challenging.

Still, RSSI based indoor localization systems remains an active field of research. A multitude of approaches and algorithms have been proposed to gain accuracy in position estimations. The most common of these techniques are explored in this report. Based on previous work at The Polytechnic University of Catalonia, the Telos hardware has been integrated successfully with existing software to form local wireless sensor networks for indoor localization. We present applications developed on top of TinyOS, an operating system for embedded systems. These applications serve as a platform for related future work at The Polytechnic University of Catalonia and elsewhere.

• 330.
Politecnico di Torino, Italy.
Chalmers University of Technology, Sweden. Technical University of Madrid, Spain.
Uniformly reweighted belief propagation for distributed Bayesian hypothesis testing2011Ingår i: Proc. of IEEE Statistical Signal Processing Workshop (SSP), 2011, s. 733-736Konferensbidrag (Refereegranskat)

Belief propagation (BP) is a technique for distributed inference in wireless networks and is often used even when the underlying graphical model contains cycles. In this paper, we propose a uniformly reweighted BP scheme that reduces the impact of cycles by weighting messages by a constant “edge appearance probability” ρ ≤ 1. We apply this algorithm to distributed binary hypothesis testing problems (e.g., distributed detection) in wireless networks with Markov random field models. We demonstrate that in the considered setting the proposed method outperforms standard BP, while maintaining similar complexity. We then show that the optimal ρ can be approximated as a simple function of the average node degree, and can hence be computed in a distributed fashion through a consensus algorithm.

• 331.
S2, Chalmers University. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Amplifier-Aware Multiple-Input Multiple-Output Power Allocation2013Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 17, nr 6, s. 1112-1115Artikel i tidskrift (Refereegranskat)

We propose multiple-input multiple-output (MIMO)transmitter power allocation which takes dissipation in the power amplifiers into account. We derive the equations of the generalproblem with full channel state information (CSI), discuss its challenges, and supply solutions in two special cases, namely fora multiple-input single-output channel with a linear beamformer constraint, and for a parallel MIMO channel. The proposed algorithms show substantial gains in terms of rate and total consumed power compared to previous state of the art over awide range of parameter settings, and have low computational complexities.

• 332.
School of Electrical Engineering, KTH. School of Electrical Engineering, KTH. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Joint Source-Channel Coding for the MIMO Broadcast Channel2012Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, nr 4, s. 2085-2090Artikel i tidskrift (Refereegranskat)

We investigate the problem of broadcasting analog sources to several users using short codes,employing several antennas at both the transmitter and the receiver, and channel-optimized quantization.Our main objective is to minimize the sum mean square error distortion. A joint multi-user encoder, aswell as a structured encoder with separate encoders for the different users, are proposed. The ﬁrst encoderoutperforms the latter, which in turn offers large improvements compared to state-of-the-art, over a widerange of channel signal-to-noise ratios. Our proposed methods handle bandwidth expansion, i.e., usageof more channel than source dimensions, automatically. We also derive a lower bound on the distortion.

• 333.
School of Electrical Engineering, KTH. School of Electrical Engineering, KTH. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
Joint Source-Channel Coding for the MIMO Broadcast Channel2012Dataset

We investigate the problem of broadcasting analog sources to several users using short codes,employing several antennas at both the transmitter and the receiver, and channel-optimized quantization.Our main objective is to minimize the sum mean square error distortion. A joint multi-user encoder, aswell as a structured encoder with separate encoders for the different users, are proposed. The ﬁrst encoderoutperforms the latter, which in turn offers large improvements compared to state-of-the-art, over a widerange of channel signal-to-noise ratios. Our proposed methods handle bandwidth expansion, i.e., usageof more channel than source dimensions, automatically. We also derive a lower bound on the distortion.

• 334.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan. Royal Institute of Technology, Stockholm, Sweden.
Joint Source-Channel Decoding over MIMOChannels Based on Partial Marginalization2012Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 60, nr 12, s. 6734-6739Artikel i tidskrift (Refereegranskat)

We investigate fast joint source-channel decoding employed for communication over frequency-flat and frequency selective block-fading multiple-input multiple-output channels. Our setting has applications for communication with short codes under low-latency constraints. The case of no transmitter channel state information is considered.

We propose a partial marginalization decoder that allows performance to be traded for computational complexity, by adjusting a user parameter. By tuning this parameter to its maximum value, the minimum mean square error (MMSE)decoder is obtained. In the conducted simulations, the proposed scheme almost achieves the MMSE performance for a wide range of the channel signal-to-noise ratios, with significant reductions in computational complexity.

• 335.
Chalmers University of Technology, Gothenburg, Sweden. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska högskolan.
Amplifier-Aware Multiple-Input Single-Output Capacity2014Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, nr 1, s. 913-919Artikel i tidskrift (Refereegranskat)

We investigate multiple-input single-output channel capacity taking dissipation in the power amplifiers into account. We consider the case of a fixed channel with full channel state information (CSI) at both the transmitter and receiver. The capacity expression is given on closed form, and we show that the optimal solution is antenna selection. An algorithm for finding minimum consumed power for any given mutual information is further developed, and we show that the power-mutual information pair is capacity-achieving. We also investigate the ergodic Rayleigh fading channel with full CSI at the receiver and no instantaneous CSI at the transmitter. We devise a numerical approach which finds the global optimum given a quantization of the space of possible allocated powers. We further show that down to the simulation precision, the ergodic Rayleigh fading solution again is antenna selection. It is shown that the allocation algorithms have low computational complexity and give significant rate and total consumed power gains in comparison to previous state of the art.

• 336.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska högskolan.
Warehouse management of promotional clothing2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)

MSB, myndigheten för samhällsskydd och beredskap, är en svensk myndighet vars uppgift är att hjälpa till vid kriser och katastrofer samt att informera samhället för att vara mer förberedda inför katastrofer. För att kunna agera snabbt har MSB ett stort lager med materiel. En av de mest frekventa produktgrupperna som används är profilkläderna. I nuläget beställs profilkläderna främst baserat på magkänsla och det finns inte så mycket tanke bakom beställningarna. MSB vill nu förbättra sin lagerstyrning för att få en mer effektiv lagerhållning. Målet med detta arbete är därmed att skapa ett lagerstyrningssystem för MSB:s profilkläder. För att genomföra arbetet samlades data gällande inköp och efterfrågan in från MSB:s lagersystem. Denna data bearbetades sedan genom att den delades in i intervall och analyserades. För respektive produkt analyserades efterfrågemönster. Det beräknades även totalt antal uttagna produkter, medelvärdet för efterfrågan under en ledtidsperiod, standardavvikelsen för efterfrågan under en ledtidsperiod, årsefterfrågan, ekonomisk orderkvantitet, säkerhetslager, beställningspunkt och återfyllnadsnivå utifrån vissa antaganden. Dessa metoder analyserades för att identifiera det mest fördelaktiga lagerstyrningssystemet för MSB:s profilkläder. Även olika principer för prognostisering behandlades för att utreda hur den framtida efterfrågan av dessa produkter borde prognostiseras. Rekommendationen som tagits fram genom beräkningarna och analysen är att MSB bör använda sig av ett återfyllnadssystem för beställning av profilkläder. I MSB:s fall innebär detta att lagernivån ska undersökas två gånger om året och de olika profilkläderna ska sedan beställas upp till en förutbestämd nivå baserat på historisk efterfrågan och säkerhetslagret. I MSB:s fall bedömdes säkerhetslagret som extra viktigt eftersom efterfrågan är väldigt ojämn och osäker. Att ha ett större säkerhetslager bidrar bland annat till högre kostnader men i MSB:s fall anses en hög beredskap vara viktigare än att minimera kostnaderna.

• 337.
Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Informatik. Linköpings universitet, Filosofiska fakulteten.
ICT-Enabled Citizen Co-production in Excluded Areas – Using Volunteers in Emergency Response2019Ingår i: Electronic Participation: 11th IFIP WG 8.5 International Conference, ePart 2019, San Benedetto Del Tronto, Italy, September 2–4, 2019 Proceedings / [ed] Panos Panagiotopoulos, Noella Edelmann, Olivier Glassey, Gianluca Misuraca, Peter Parycek, Thomas Lampoltshammer and Barbara Re, Cham: Springer, 2019, s. 87-101Konferensbidrag (Refereegranskat)

One of many contemporary public-sector challenges is the increasing socio-economic gaps and excluded areas in many cities worldwide. This study explores ICT-enabled citizen co-production using volunteers as first responders in excluded areas near Stockholm, the capital of Sweden. The study indicates that these volunteers can make a major difference if arriving first at an emergency site, e.g. saving lives by administering CPR and extinguishing fires before they spread. Major challenges relate to individual versus collective engagement, gender aspects and language barriers. Current ICT support, in the form of text messages or a basic app, is deemed sufficient but, for the initiative to expand and enable long-term effective engagement, calibrated solutions matching competence, role and language with incident and area are needed. In a public-sector innovation context, the study highlights the need for future research on digitalized co-production with an explicit focus on the ICT artifact and its co-creation artifact as catalysts for change. In relation to this, this study confirms previous research arguing for the merging of policy science and information systems research in an era of rapid digitalized public-sector transformation, but adds that they need to be complemented by perspectives from sociology, e.g. on gender and ethnicity, in initiatives involving citizens in excluded areas.

• 338.
Signal Reconstruction Algorithms for Time-Interleaved ADCs2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

An analog-to-digital converter (ADC) is a key component in many electronic systems. It is used to convert analog signals to the equivalent digital form. The conversion involves sampling which is the process of converting a continuous-time signal to a sequence of discrete-time samples, and quantization in which each sampled value is represented using a finite number of bits. The sampling rate and the effective resolution (number of bits) are two key ADC performance metrics. Today, ADCs form a major bottleneck in many applications like communication systems since it is difficult to simultaneously achieve high sampling rate and high resolution. Among the various ADC architectures, the time-interleaved analog-to-digital converter (TI-ADC) has emerged as a popular choice for achieving very high sampling rates and resolutions. At the principle level, by interleaving the outputs of M identical channel ADCs, a TI-ADC could achieve the same resolution as that of a channel ADC but with M times higher bandwidth. However, in practice, mismatches between the channel ADCs result in a nonuniformly sampled signal at the output of a TI-ADC which reduces the achievable resolution. Often, in TIADC implementations, digital reconstructors are used to recover the uniform-grid samples from the nonuniformly sampled signal at the output of the TI-ADC. Since such reconstructors operate at the TI-ADC output rate, reducing the number of computations required per corrected output sample helps to reduce the power consumed by the TI-ADC. Also, as the mismatch parameters change occasionally, the reconstructor should support online reconfiguration with minimal or no redesign. Further, it is advantageous to have reconstruction schemes that require fewer coefficient updates during reconfiguration. In this thesis, we focus on reducing the design and implementation complexities of nonrecursive finite-length impulse response (FIR) reconstructors. We propose efficient reconstruction schemes for three classes of nonuniformly sampled signals that can occur at the output of TI-ADCs.

Firstly, we consider a class of nonuniformly sampled signals that occur as a result of static timing mismatch errors or due to channel mismatches in TI-ADCs. For this type of nonuniformly sampled signals, we propose three reconstructors which utilize a two-rate approach to derive the corresponding single-rate structure. The two-rate based reconstructors move part of the complexity to a symmetric filter and also simplifies the reconstruction problem. The complexity reduction stems from the fact that half of the impulse response coefficients of the symmetric filter are equal to zero and that, compared to the original reconstruction problem, the simplified problem requires only a simpler reconstructor.

Next, we consider the class of nonuniformly sampled signals that occur when a TI-ADC is used for sub-Nyquist cyclic nonuniform sampling (CNUS) of sparse multi-band signals. Sub-Nyquist sampling utilizes the sparsities in the analog signal to sample the signal at a lower rate. However, the reduced sampling rate comes at the cost of additional digital signal processing that is needed to reconstruct the uniform-grid sequence from the sub-Nyquist sampled sequence obtained via CNUS. The existing reconstruction scheme is computationally intensive and time consuming and offsets the gains obtained from the reduced sampling rate. Also, in applications where the band locations of the sparse multi-band signal can change from time to time, the reconstructor should support online reconfigurability. Here, we propose a reconstruction scheme that reduces the computational complexity of the reconstructor and at the same time, simplifies the online reconfigurability of the reconstructor.

Finally, we consider a class of nonuniformly sampled signals which occur at the output of TI-ADCs that use some of the input sampling instants for sampling a known calibration signal. The samples corresponding to the calibration signal are used for estimating the channel mismatch parameters. In such TI-ADCs, nonuniform sampling is due to the mismatches between the channel ADCs and due to the missing input samples corresponding to the sampling instants reserved for the calibration signal. We propose three reconstruction schemes for such nonuniformly sampled signals and show using design examples that, compared to a previous solution, the proposed schemes require substantially lower computational complexity.

1. Two-rate based low-complexity time-varying discrete-time FIR reconstructors for two-periodic nonuniformly sampled signals
Öppna denna publikation i ny flik eller fönster >>Two-rate based low-complexity time-varying discrete-time FIR reconstructors for two-periodic nonuniformly sampled signals
2012 (Engelska)Ingår i: Sampling Theory in Signal and Image Processing, ISSN 1530-6429, Vol. 11, nr 2-3, s. 195-220Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

This paper deals with time-varying finite-length impulse response (FIR) filters used for reconstruction of two-periodic nonuniformly sampled signals. The complexity of such reconstructorsincreases as their bandwidth approaches the whole Nyquist band. Reconstructor design that yields minimum reconstructor order requires expensive online redesign while those methods that simplify online redesign result in higher reconstructor complexity. This paper utilizes a two-rate approach to derive a single-rate structure where part of the complexity of the reconstructor is moved to a symmetric filter so as to reduce the number of multipliers. The symmetric filter is designed such that it can be used for all time-skew errors within a certain range, thereby reducing the number of coefficients that need online redesign. The basic two-rate based reconstructor is further extended to completely remove the need for online redesign at the cost of a slight increase in the total number of multipliers.

##### Ort, förlag, år, upplaga, sidor
Sampling Publishing, 2012
##### Nyckelord
Finite-length impulse response (FIR) filters, least-squares design, two-rate approach, periodic nonuniform sampling, time-interleaved analog-to-digital converters (TI-ADCs), reconstruction filters
##### Nationell ämneskategori
Signalbehandling
##### Identifikatorer
urn:nbn:se:liu:diva-105470 (URN)2-s2.0-84896442526 (Scopus ID)
##### Forskningsfinansiär
2. Efficient signal reconstruction scheme for M-channel time-interleaved ADCs
Öppna denna publikation i ny flik eller fönster >>Efficient signal reconstruction scheme for M-channel time-interleaved ADCs
2013 (Engelska)Ingår i: Analog Integrated Circuits and Signal Processing, ISSN 0925-1030, E-ISSN 1573-1979, Vol. 77, nr 2, s. 113-122Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

In time-interleaved analog-to-digital converters (TI-ADCs), the timing mismatches between the channels result in a periodically nonuniformly sampled sequence at the output. Such nonuniformly sampled output limits the achievable resolution of the TI-ADC. In order to correct the errors due to timing mismatches, the output of the TI-ADC is passed through a digital time-varying finite-length impulse response reconstructor. Such reconstructors convert the nonuniformly sampled output sequence to a uniformly spaced output. Since the reconstructor runs at the output rate of the TI-ADC, it is beneficial to reduce the number of coefficient multipliers in the reconstructor. Also, it is advantageous to have as few coefficient updates as possible when the timing errors change. Reconstructors that reduce the number of multipliers to be updated online do so at a cost of increased number of multiplications per corrected output sample. This paper proposes a technique which can be used to reduce the number of reconstructor coefficients that need to be updated online without increasing the number of multiplications per corrected output sample.

##### Ort, förlag, år, upplaga, sidor
Springer, 2013
##### Nyckelord
Finite-length impulse response (FIR) filters, Least-squares design, Two-rate approach, Periodically nonuniform sampling, Time-interleaved analog-to-digital converters (TI-ADCs), Reconstruction filters
##### Nationell ämneskategori
Signalbehandling
##### Identifikatorer
urn:nbn:se:liu:diva-100965 (URN)10.1007/s10470-013-0115-x (DOI)000326453400004 ()
##### Forskningsfinansiär
3. Low-complexity two-rate based multivariate impulse response reconstructor for time-skew error correction in m-channel time-interleaved ADCs
Öppna denna publikation i ny flik eller fönster >>Low-complexity two-rate based multivariate impulse response reconstructor for time-skew error correction in m-channel time-interleaved ADCs
2013 (Engelska)Ingår i: IEEE International Symposium on Circuits and Systems (ISCAS), 2013, IEEE , 2013, s. 2936-2939Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

Nonuniform sampling occurs in time-interleaved analog-to-digital converters (TI-ADC) due to timing mismatches between the individual channel analog-to-digital converters (ADCs). Such nonuniformly sampled output will degrade the achievable resolution in a TI-ADC. To restore the degraded performance, digital time-varying reconstructors can be used at the output of the TI-ADC, which in principle, converts the nonuniformly sampled output sequence to a uniformly sampled output. As the bandwidth of these reconstructors increases, their complexity also increases rapidly. Also, since the timing errors change occasionally, it is important to have a reconstructor architecture that requires fewer coefficient updates when the value of the timing error changes. Multivariate polynomial impulse response reconstructor is an attractive option for an M-channel reconstructor. If the channel timing error varies within a certain limit, these reconstructors do not need any online redesign of their impulse response coefficients. This paper proposes a technique that can be applied to multivariate polynomial impulse response reconstructors in order to further reduce the number of fixed-coefficient multipliers, and thereby reduce the implementation complexity.

IEEE, 2013
##### Serie
IEEE International Symposium on Circuits and Systems, ISSN 0271-4310
##### Nationell ämneskategori
Teknik och teknologier
##### Identifikatorer
urn:nbn:se:liu:diva-106537 (URN)10.1109/ISCAS.2013.6572494 (DOI)000332006803036 ()978-1-4673-5760-9 (ISBN)
##### Konferens
IEEE International Symposium on Circuits and Systems (ISCAS), 19-23 May 2013, Beijing, China
4. Efﬁcient Recovery of Sub-Nyquist Sampled Sparse Multi-Band Signals Using Reconﬁgurable Multi-Channel Analysis and Modulated Synthesis Filter Banks
Öppna denna publikation i ny flik eller fönster >>Efﬁcient Recovery of Sub-Nyquist Sampled Sparse Multi-Band Signals Using Reconﬁgurable Multi-Channel Analysis and Modulated Synthesis Filter Banks
2015 (Engelska)Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, nr 19, s. 5238-5249Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Sub-Nyquist cyclic nonuniform sampling (CNUS) of a sparse multi-band signal generates a nonuniformly sampled signal. Assuming that the corresponding uniformly sampled signal satisfies the Nyquist sampling criterion, the sequence obtained via CNUS can be passed through a reconstructor to recover the missing uniform-grid samples. In order to recover the missing uniform-grid samples, the sequence obtained via CNUS is passed through a reconstructor. At present, these reconstructors have very high design and implementation complexity that offsets the gains obtained due to sub-Nyquist sampling. In this paper, we propose a scheme that reduces the design and implementation complexity of the  reconstructor. In contrast to the existing reconstructors which use only a multi-channel synthesis filter bank (FB), the proposed reconstructor utilizes both analysis and synthesis FBs which makes it feasible to achieve an order-of-magnitude reduction of the complexity. The analysis filters are implemented using polyphase networks whose branches are allpass filters with distinct fractional delays and phase shifts. In order to reduce both the design and the implementation complexity of the  synthesis FB, the synthesis filters are implemented using a cosine-modulated FB. In addition to the reduced complexity of the reconstructor, the proposed multi-channel recovery scheme also supports online reconfigurability which is required in flexible (multi-mode) systems where the user subband locations vary with time.

IEEE, 2015
##### Nyckelord
Sub-Nyquist sampling, sparse multi-band signals, reconstruction, nonuniform sampling, time-interleaved analog-to-digital converters, ﬁlter banks
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-117824 (URN)10.1109/TSP.2015.2451104 (DOI)000360852200017 ()
5. A sub-band based reconstructor for M-channel time-interleaved ADCs with missing samples
Öppna denna publikation i ny flik eller fönster >>A sub-band based reconstructor for M-channel time-interleaved ADCs with missing samples
2014 (Engelska)Ingår i: 2014 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING (ICASSP), IEEE conference proceedings, 2014Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

This paper proposes a scheme for the recovery of a uniformly sampled sequence from the output of a time-interleaved analog-to-digital converter (TI-ADC) with static time-skew errors and missing samples. Nonuniform sampling occurs due to timing mismatches between the individual channel ADCs and also due to missing input samples as some of the sampling instants are reserved for estimating the mismatches in the TI-ADC. In addition to using a non-recursive structure, the proposed reconstruction scheme supports online reconfigurability and reduces the computational complexity of the reconstructor as compared to a previous solution.

##### Ort, förlag, år, upplaga, sidor
IEEE conference proceedings, 2014
##### Serie
International Conference on Acoustics Speech and Signal Processing ICASSP, ISSN 1520-6149
##### Nationell ämneskategori
Signalbehandling
##### Identifikatorer
urn:nbn:se:liu:diva-103931 (URN)10.1109/ICASSP.2014.6854378 (DOI)000343655304030 ()978-1-4799-2893-4 (ISBN)
##### Konferens
IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP 2014), Florence, Italy, May 4-9, 2014
6. Two reconstructors for M-channel time-interleaved ADCs with missing samples
Öppna denna publikation i ny flik eller fönster >>Two reconstructors for M-channel time-interleaved ADCs with missing samples
2014 (Engelska)Ingår i: IEEE 12th International New Circuits and Systems Conference (NEWCAS), 2014, IEEE conference proceedings, 2014, s. 41-44Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

In this paper, we explore two nonrecursive reconstructors which recover the uniform-grid samples from the output of a time-interleaved analog-to-digital converter (TI-ADC) that uses some of the sampling instants for estimating the mismatches in the TI-ADC. Nonuniform sampling occurs due to timing mismatches between the individual channel ADCs and also due to missing input samples. Compared to a previous solution, the reconstructors presented here offer substantially lower computational complexity.

##### Ort, förlag, år, upplaga, sidor
IEEE conference proceedings, 2014
##### Nationell ämneskategori
Signalbehandling
##### Identifikatorer
urn:nbn:se:liu:diva-106048 (URN)10.1109/NEWCAS.2014.6933980 (DOI)000363906700011 ()
##### Konferens
12th IEEE International New Circuits and Systems Conference (NEWCAS), Trois-Rivières, Canada, June 22-25, 2014.
7. Prefilter-Based Reconfigurable Reconstructor for Time-Interleaved ADCs With Missing Samples
Öppna denna publikation i ny flik eller fönster >>Prefilter-Based Reconfigurable Reconstructor for Time-Interleaved ADCs With Missing Samples
2015 (Engelska)Ingår i: IEEE Transactions on Circuits and Systems - II - Express Briefs, ISSN 1549-7747, E-ISSN 1558-3791, Vol. 62, nr 4, s. 392-396Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

This brief proposes a reconstruction scheme for the compensation of frequency-response mismatch errors at the output of a time-interleaved analog-to-digital converter (TI-ADC) with missing samples. The missing samples are due to sampling instants reserved for estimating the channel mismatch errors in the TI-ADC. Compared with previous solutions, the proposed scheme offers substantially lower computational complexity.

##### Ort, förlag, år, upplaga, sidor
IEEE Press, 2015
##### Nyckelord
Reconstruction, frequency-response mismatch errors, time-interleaved analog-to-digital converters, reconﬁgurable reconstructors
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-117769 (URN)10.1109/TCSII.2014.2387651 (DOI)000352306200016 ()
• 339.
Efﬁcient Recovery of Sub-Nyquist Sampled Sparse Multi-Band Signals Using Reconﬁgurable Multi-Channel Analysis and Modulated Synthesis Filter Banks2015Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 63, nr 19, s. 5238-5249Artikel i tidskrift (Refereegranskat)

Sub-Nyquist cyclic nonuniform sampling (CNUS) of a sparse multi-band signal generates a nonuniformly sampled signal. Assuming that the corresponding uniformly sampled signal satisfies the Nyquist sampling criterion, the sequence obtained via CNUS can be passed through a reconstructor to recover the missing uniform-grid samples. In order to recover the missing uniform-grid samples, the sequence obtained via CNUS is passed through a reconstructor. At present, these reconstructors have very high design and implementation complexity that offsets the gains obtained due to sub-Nyquist sampling. In this paper, we propose a scheme that reduces the design and implementation complexity of the  reconstructor. In contrast to the existing reconstructors which use only a multi-channel synthesis filter bank (FB), the proposed reconstructor utilizes both analysis and synthesis FBs which makes it feasible to achieve an order-of-magnitude reduction of the complexity. The analysis filters are implemented using polyphase networks whose branches are allpass filters with distinct fractional delays and phase shifts. In order to reduce both the design and the implementation complexity of the  synthesis FB, the synthesis filters are implemented using a cosine-modulated FB. In addition to the reduced complexity of the reconstructor, the proposed multi-channel recovery scheme also supports online reconfigurability which is required in flexible (multi-mode) systems where the user subband locations vary with time.

• 340.
Feasibility Study for Wireless Control on The Countermeasure Dispenser System2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)

Electrical wiring on board aircraft has raised serious weight and safety concerns in the aerospace industry. Wires are antenna. It may also cause interference to radio-based systems on the aircraft, or, in the case of military aircraft, create a "signature" that can be detected by enemy receivers. Wireless application in avionic system helps reducing the total weight and reconfigurable of the aircraft; hence, lower the fuel costs, installation cost and maintenance costs, as well as the “signature” of the aircraft. The focus of this thesis, therefore, is to study the feasibility of different wireless standards, namely Wi-Fi, Bluetooth and ultra-wide band (UWB), on replacing the wired data connection in the EW countermeasure or chaff/flare dispenser systems.

The study was constructed under the supervision of the department of Electronic Defense System, Saab AB in Järfalla, Stockholm. The discussion will be based on the resource availability, the reliability, the stability and the security of the wireless system relative to an avionic application; i.e., whether wireless links will negatively affect the overall reliability and safety of the aircrafts. Due to the theoretical studies and results from the simulation, we studied the feasibility issue and concluded that UWB is the most appropriate choice of wireless communication for non-critical aerospace applications, comparing with Wi-Fi and Bluetooth. UWB links can have reasonable immunity to interferences, low interference to other on-board wireless systems, and good security performance.

• 341.
IUST, Sch Elect Engn, Tehran 1684613114, Iran.
IUST, Sch Elect Engn, Tehran 1684613114, Iran. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
Subverting Massive MIMO by Smart Jamming2016Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 5, nr 1, s. 20-23Artikel i tidskrift (Refereegranskat)

We consider uplink transmission of a massive multiuser multiple-input multiple-output (MU-MIMO) system in the presence of a smart jammer. The jammer aims to degrade the sum spectral efficiency of the legitimate system by attacking both the training and data transmission phases. First, we derive a closed-form expression for the sum spectral efficiency by taking into account the presence of a smart jammer. Then, we determine how a jammer with a given energy budget should attack the training and data transmission phases to induce the maximum loss to the sum spectral efficiency. Numerical results illustrate the impact of optimal jamming specifically in the large limit of the number of base station (BS) antennas.

• 342.
On the performance of Massive MIMO systems with single carrier transmission and phase noise2013Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)

In the last decade we have experienced a rapid increase in the demand for high data rates over cellular networks. This increase has been partly satisfied by the introduction of multi-user multiple-input multiple-output (MU-MIMO). In such systems, the base station (BS) is equipped with multiple antennas and the users share the time-frequency resources. However, modern communication systems are highly power inefficient. Further, the increase in demand for higher data rates is expected to accelerate in the years to come due to the popularity of mobile devices like smartphones and tablets. Hence, next generation cellular systems arerequired to exhibit high energy efficiency as well as low power  consumption. Recently, it has been shown that the deployment of a large excess of base station (BS) antennas in comparison to the served users can be a promising candidate to meet these contradictory requirements. These systems are termed as Massive MIMO. When the number of BS antennas grows large, the channels between different users become orthogonal and low complexity transceiver processing exhibits sum-rate performance that is close to optimal. In order to realize the promised gains of Massive MIMO systems, it is required that power efficient and inexpensive components are used. In contemporary cellular systems, multi-carrier transmission is used since it facilitates simple equalization at the receiver side. However, multi-carrier signals exhibit high peak-to-average-power-ratio (PAPR) and require expensive highly linear power amplifiers. Power amplifiers in this regime are also very power inefficient. On the other hand single carrier signals exhibit lower PAPR and are suitable for signal design that is more robust to non-linear power amplifiers. Further, single-carrier signals are less vulnerable to hardware impairments, such as phase noise. In this thesis we study the fundamental limits of Massive MIMO systems in terms of sum-rate performance with single-carrier transmission and phase noise and provide important insight on the design of Massive MIMO under these scenarios.

1. On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
Öppna denna publikation i ny flik eller fönster >>On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
2012 (Engelska)Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 1, nr 4, s. 276-279Artikel i tidskrift (Övrigt vetenskapligt) Published
##### Abstract [en]

A single carrier transmission scheme is presentedfor the frequency selective multi-user (MU) multiple-input singleoutput(MISO) Gaussian Broadcast Channel (GBC) with a basestation (BS) having M antennas and K single antenna users.The proposed transmission scheme has low complexity andfor M ≫ K it is shown to achieve near optimal sum-rateperformance at low transmit power to receiver noise power ratio.Additionally, the proposed transmission scheme results in anequalization-free receiver and does not require any MU resourceallocation and associated control signaling overhead. Also, thesum-rate achieved by the proposed transmission scheme is shownto be independent of the channel power delay profile (PDP). Interms of power efficiency, the proposed transmission scheme alsoexhibits an O(M) array power gain. Simulations are used toconfirm analytical observations.

##### Ort, förlag, år, upplaga, sidor
Institute of Electrical and Electronics Engineers (IEEE), 2012
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-80173 (URN)10.1109/WCL.2012.041612.120046 (DOI)
##### Anmärkning

© Copyright 2012 IEEE Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.

2. Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
Öppna denna publikation i ny flik eller fönster >>Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
2015 (Engelska)Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, s. 711-723Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an excess of base station (BS) antennas (Massive MIMO) offer unprecedented multiplexing gains and radiated energy efficiency. Oscillator phase noise is introduced in the transmitter and receiver radio frequency chains and severely degrades the performance of communication systems. We study the effect of oscillator phase noise in frequency-selective Massive MIMO systems with imperfect channel state information (CSI) and M BS antennas. In particular, we consider two distinct operation modes, namely when the phase noise processes at the BS antennas are identical (synchronous operation) and when they are independent (non-synchronous operation). We analyze a linear and low-complexity time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both operation modes we derive a lower bound on the sum-capacity and we compare the performance of the two modes. Based on the derived achievable sum-rate, we show that with the proposed receive processing an O($\sqrt{M}$) array gain is achievable. Due to the phase noise drift the estimated effective channel becomes progressively outdated. Therefore, phase noise effectively limits the length of the interval used for data transmission and the number of scheduled users. The derived achievable rates provide insights into the optimum choice of the data interval length and the number of scheduled users.

IEEE, 2015
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-97477 (URN)10.1109/TWC.2014.2359018 (DOI)000349674800010 ()
##### Anmärkning

Manuscript received March 5, 2014; revised July 10, 2014; accepted September 6, 2014. Date of publication September 18, 2014; date of current version February 6, 2015. This work was supported in part by the Swedish Foundation for Strategic Research and in part by ELLIIT. The work of S. K. Mohammed was supported by the Science and Engineering Research Board, Department of Science and Technology, Government of India. This paper was presented in part at the 50th Allerton Conference on Communication, Control and Computing, Urbana-Champaign, IL, USA, October 2012. The associate editor coordinating the review of this paper and approving it for publication was L. Sanguinetti.

3. Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
Öppna denna publikation i ny flik eller fönster >>Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
2013 (Engelska)Ingår i: 2013 ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, 2013, s. 1004-1008Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

The effect of oscillator phase noise on the sum-rate performance of large multi-user multiple-input multiple-output (MU-MIMO) systems, termed as Massive MIMO, is studied. A Rayleigh fading MU-MIMO uplink channel is considered, where channel state information (CSI) is acquired via training. The base station (BS), which is equipped with an excess of antenna elements, M, uses the channel estimate to perform zero-forcing (ZF) detection. A lower bound on the sum-rate performance is derived. It is shown that the proposed receiver structure exhibits an O($\sqrt{M}$) array power gain. Additionally, the proposed receiver is compared with earlier studies that employ maximum ratio combining and it is shown that it can provide significant sum-rate performance gains at the medium and high signal-to-noise-ratio (SNR) regime. Further, the expression of the achievable sum rate provides new insights on the effect of various parameters on the overall system performance.

##### Serie
ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, ISSN 1058-6393
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-97478 (URN)10.1109/ACSSC.2013.6810441 (DOI)000341772900184 ()978-1-4799-2390-8 (ISBN)
##### Konferens
47th Asilomar Conference on Signals, Systems and Computers
• 343.
Phase Noise and Wideband Transmission in Massive MIMO2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)

In the last decades the world has experienced a massive growth in the demand for wireless services. The recent popularity of hand-held devices with data exchange capabilities over wireless networks, such as smartphones and tablets, increased the wireless data traffic even further. This trend is not expected to cease in the foreseeable future. In fact, it is expected to accelerate as everyday apparatus unrelated with data communications, such as vehicles or household devices, are foreseen to be equipped with wireless communication capabilities.

Further, the next generation wireless networks should be designed such that they have increased spectral and energy efficiency, provide uniformly good service to all of the accommodated users and handle many more devices simultaneously. Massive multiple-input multiple-output (Massive MIMO) systems, also termed as large-scale MIMO, very large MIMO or full-dimension MIMO, have recently been proposed as a candidate technology for next generation wireless networks. In Massive MIMO, base stations (BSs) with a large number of antenna elements serve simultaneously only a few tens of single antenna, non-cooperative users. As the number of BS antennas grow large, the normalized channel vectors to the users become pairwise asymptotically orthogonal and, therefore, simple linear processing techniques are optimal. This is substantially different from the current design of contemporary cellular systems, where BSs are equipped with a few antennas and the optimal processing is complex. Consequently, the need for redesign of the communication protocols is apparent.

The deployment of Massive MIMO requires the use of many inexpensive and, potentially, off-the-shelf hardware components. Such components are likely to be of low quality and to introduce distortions to the information signal. Hence, Massive MIMO must be robust against the distortions introduced by the hardware impairments. Among the most important hardware impairments is phase noise, which is introduced by local oscillators (LOs) at the BS and the user terminals. Phase noise is a phenomenon of particular importance since it acts multiplicatively on the desired signal and rotates it by some random and unknown argument. Further, the promised gains of Massive MIMO can be reaped by coherent combination of estimated channel impulse responses at the BS antennas. Phase noise degrades the quality of the estimated channel impulse responses and impedes the coherent combination of the received waveforms.

In this dissertation, wideband transmission schemes and the effect of phase noise on Massive MIMO are studied. First, the use of a low-complexity single-carrier precoding scheme for the broadcast channel is investigated when the number of BS antennas is much larger than the number of served users. A rigorous, closed-form lower bound on the achievable sum-rate is derived and a scaling law on the potential radiated energy savings is stated. Further, the performance of the proposed scheme is compared with a sum-capacity upper bound and with a bound on the performance of the contemporary multi-carrier orthogonal frequency division multiplexing (OFDM) transmission.

Second, the effect of phase noise on the achievable rate performance of a wideband Massive MIMO uplink with time-reversal maximum ratio combining (TRMRC) receive processing is investigated. A rigorous lower bound on the achievable sum-rate is derived and a scaling law on the radiated energy efficiency is established. Two distinct LO configurations at the BS, i.e., the common LO (synchronous) operation and the independent LO (non-synchronous) operation, are analyzed and compared. It is concluded that the non-synchronous operation is preferable due to an averaging of the independent phase noise sources. Further, a progressive degradation of the achievable rate due to phase noise is observed. A similar study is extended to a flat fading uplink with zero-forcing (ZF) receiver at the BS.

The fundamental limits of data detection in a phase-noise-impaired uplink are also studied, when the channel impulse responses are estimated via uplink training. The corresponding maximum likelihood (ML) detector is provided for the synchronous and non-synchronous operations and for a general parameterization of the phase noise statistics. The symbol error rate (SER) performance at the high signal-to-noise ratio (SNR) of the detectors is studied. Finally, rigorous lower bounds on the achievable rate of a Massive MIMO-OFDM uplink are derived and scaling laws on the radiated energy efficiency are stated.

1. On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
Öppna denna publikation i ny flik eller fönster >>On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
2012 (Engelska)Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 1, nr 4, s. 276-279Artikel i tidskrift (Övrigt vetenskapligt) Published
##### Abstract [en]

A single carrier transmission scheme is presentedfor the frequency selective multi-user (MU) multiple-input singleoutput(MISO) Gaussian Broadcast Channel (GBC) with a basestation (BS) having M antennas and K single antenna users.The proposed transmission scheme has low complexity andfor M ≫ K it is shown to achieve near optimal sum-rateperformance at low transmit power to receiver noise power ratio.Additionally, the proposed transmission scheme results in anequalization-free receiver and does not require any MU resourceallocation and associated control signaling overhead. Also, thesum-rate achieved by the proposed transmission scheme is shownto be independent of the channel power delay profile (PDP). Interms of power efficiency, the proposed transmission scheme alsoexhibits an O(M) array power gain. Simulations are used toconfirm analytical observations.

##### Ort, förlag, år, upplaga, sidor
Institute of Electrical and Electronics Engineers (IEEE), 2012
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-80173 (URN)10.1109/WCL.2012.041612.120046 (DOI)
##### Anmärkning

© Copyright 2012 IEEE Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.

2. Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
Öppna denna publikation i ny flik eller fönster >>Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise
2015 (Engelska)Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, s. 711-723Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an excess of base station (BS) antennas (Massive MIMO) offer unprecedented multiplexing gains and radiated energy efficiency. Oscillator phase noise is introduced in the transmitter and receiver radio frequency chains and severely degrades the performance of communication systems. We study the effect of oscillator phase noise in frequency-selective Massive MIMO systems with imperfect channel state information (CSI) and M BS antennas. In particular, we consider two distinct operation modes, namely when the phase noise processes at the BS antennas are identical (synchronous operation) and when they are independent (non-synchronous operation). We analyze a linear and low-complexity time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both operation modes we derive a lower bound on the sum-capacity and we compare the performance of the two modes. Based on the derived achievable sum-rate, we show that with the proposed receive processing an O($\sqrt{M}$) array gain is achievable. Due to the phase noise drift the estimated effective channel becomes progressively outdated. Therefore, phase noise effectively limits the length of the interval used for data transmission and the number of scheduled users. The derived achievable rates provide insights into the optimum choice of the data interval length and the number of scheduled users.

IEEE, 2015
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-97477 (URN)10.1109/TWC.2014.2359018 (DOI)000349674800010 ()
##### Anmärkning

Manuscript received March 5, 2014; revised July 10, 2014; accepted September 6, 2014. Date of publication September 18, 2014; date of current version February 6, 2015. This work was supported in part by the Swedish Foundation for Strategic Research and in part by ELLIIT. The work of S. K. Mohammed was supported by the Science and Engineering Research Board, Department of Science and Technology, Government of India. This paper was presented in part at the 50th Allerton Conference on Communication, Control and Computing, Urbana-Champaign, IL, USA, October 2012. The associate editor coordinating the review of this paper and approving it for publication was L. Sanguinetti.

3. Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
Öppna denna publikation i ny flik eller fönster >>Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments
2013 (Engelska)Ingår i: 2013 ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, 2013, s. 1004-1008Konferensbidrag, Publicerat paper (Refereegranskat)
##### Abstract [en]

The effect of oscillator phase noise on the sum-rate performance of large multi-user multiple-input multiple-output (MU-MIMO) systems, termed as Massive MIMO, is studied. A Rayleigh fading MU-MIMO uplink channel is considered, where channel state information (CSI) is acquired via training. The base station (BS), which is equipped with an excess of antenna elements, M, uses the channel estimate to perform zero-forcing (ZF) detection. A lower bound on the sum-rate performance is derived. It is shown that the proposed receiver structure exhibits an O($\sqrt{M}$) array power gain. Additionally, the proposed receiver is compared with earlier studies that employ maximum ratio combining and it is shown that it can provide significant sum-rate performance gains at the medium and high signal-to-noise-ratio (SNR) regime. Further, the expression of the achievable sum rate provides new insights on the effect of various parameters on the overall system performance.

##### Serie
ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, ISSN 1058-6393
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-97478 (URN)10.1109/ACSSC.2013.6810441 (DOI)000341772900184 ()978-1-4799-2390-8 (ISBN)
##### Konferens
47th Asilomar Conference on Signals, Systems and Computers
4. ML Detection in Phase Noise Impaired SIMO Channels with Uplink Training
Öppna denna publikation i ny flik eller fönster >>ML Detection in Phase Noise Impaired SIMO Channels with Uplink Training
2016 (Engelska)Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 64, nr 1, s. 223-235Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The problem of maximum likelihood (ML) detection in training-assisted single-input multiple-output (SIMO) systems with phase noise impairments is studied for two different scenarios, i.e. the case when the channel is deterministic and known (constant channel) and the case when the channel is stochastic and unknown (fading channel). Further, two different operations with respect to the phase noise sources are considered, namely, the case of identical phase noise sources and the case of independent phase noise sources over the antennas. In all scenarios the optimal detector is derived for a very general parameterization of the phase noise distribution. Further, a high signal-to-noise-ratio (SNR) analysis is performed to show that symbol-error-rate (SER) floors appear in all cases. The SER floor in the case of identical phase noise sources (for both constant and fading channels) is independent of the number of antenna elements. In contrast, the SER floor in the case of independent phase noise sources is reduced when increasing the number of antenna elements (for both constant and fading channels). Finally, the system model is extended to multiple data channel uses and it is shown that the conclusions are valid for these setups, as well.

IEEE, 2016
##### Nationell ämneskategori
Signalbehandling
##### Identifikatorer
urn:nbn:se:liu:diva-122617 (URN)10.1109/TCOMM.2015.2498163 (DOI)000368353700021 ()
##### Anmärkning

Funding agencies: Swedish Foundation for Strategic Research (SSF); ELLIIT

5. Performance of the Massive MIMO Uplink with OFDM and Phase Noise
Öppna denna publikation i ny flik eller fönster >>Performance of the Massive MIMO Uplink with OFDM and Phase Noise
2016 (Engelska)Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 20, nr 8, s. 1595-1598Artikel i tidskrift (Refereegranskat) Published
##### Abstract [en]

The performance of multi-userMassiveMIMO-OFDMuplink systems in the presence of base station (BS) phase noise impairments is investigated. Closed-form achievable rate expressions are rigorously derived under two different operations, namely the case of a common oscillator (synchronous operation) at the BS and the case of independent oscillators at each BS antenna (non-synchronous operation). It is observed that the non-synchronous operation exhibits superior performance due to the averaging of intercarrier interference. Further, radiated power scaling lawsare derived, which are identical to the phase-noise-free case.

IEEE, 2016
##### Nationell ämneskategori
Kommunikationssystem
##### Identifikatorer
urn:nbn:se:liu:diva-127398 (URN)10.1109/LCOMM.2016.2581169 (DOI)000384642900028 ()
##### Anmärkning

Funding agencies: Swedish Foundation for Strategic Research (SSF); ELLIIT

• 344.
Optimal Detection in Training Assisted SIMO Systems with Phase Noise Impairments2015Ingår i: 2015 IEEE International Conference on Communications (ICC), IEEE Press, 2015, s. 2597-2602Konferensbidrag (Refereegranskat)

Abstract—In this paper, the problem of optimal maximum likelihood detection in a single user single-input multiple-output (SIMO) channel with phase noise at the receiver is considered. The optimal detection rules under training are derived for two operation modes, namely when the phase increments are fully correlated among the M receiver antennas (synchronous operation) and when they are independent (non-synchronous operation). The phase noise increments are parameterized by a very general distribution, which includes the Wiener phase noise model as a special case. It is proven that phase noise creates a symbol-error-rate (SER) floor for both operation modes. Inthe synchronous operation this error floor is independent of M, while it goes to zero exponentially withM in the non-synchronous operation.

• 345.
Performance of the Massive MIMO Uplink with OFDM and Phase Noise2016Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558, Vol. 20, nr 8, s. 1595-1598Artikel i tidskrift (Refereegranskat)

The performance of multi-userMassiveMIMO-OFDMuplink systems in the presence of base station (BS) phase noise impairments is investigated. Closed-form achievable rate expressions are rigorously derived under two different operations, namely the case of a common oscillator (synchronous operation) at the BS and the case of independent oscillators at each BS antenna (non-synchronous operation). It is observed that the non-synchronous operation exhibits superior performance due to the averaging of intercarrier interference. Further, radiated power scaling lawsare derived, which are identical to the phase-noise-free case.

• 346.
Achievable Rates of ZF Receivers in Massive MIMO with Phase Noise Impairments2013Ingår i: 2013 ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, 2013, s. 1004-1008Konferensbidrag (Refereegranskat)

The effect of oscillator phase noise on the sum-rate performance of large multi-user multiple-input multiple-output (MU-MIMO) systems, termed as Massive MIMO, is studied. A Rayleigh fading MU-MIMO uplink channel is considered, where channel state information (CSI) is acquired via training. The base station (BS), which is equipped with an excess of antenna elements, M, uses the channel estimate to perform zero-forcing (ZF) detection. A lower bound on the sum-rate performance is derived. It is shown that the proposed receiver structure exhibits an O($\sqrt{M}$) array power gain. Additionally, the proposed receiver is compared with earlier studies that employ maximum ratio combining and it is shown that it can provide significant sum-rate performance gains at the medium and high signal-to-noise-ratio (SNR) regime. Further, the expression of the achievable sum rate provides new insights on the effect of various parameters on the overall system performance.

• 347.
Effect of Oscillator Phase Noise on Uplink Performance of Large MU-MIMO Systems2012Ingår i: Proceedings of the 50th Annual Allerton Conference on Communication, Control, and Computing,, IEEE , 2012, s. 1190-1197Konferensbidrag (Refereegranskat)

The effect of oscillator phase noise on the sumrate performance of a frequency selective multi-user multipleinputmultiple-output (MU-MIMO) uplink channel is studiedunder imperfect channel state information. A maximum ratiocombining detection strategy is employed by the base station(BS) (having a large antenna array of M elements), and ananalytical expression of a lower bound on the sum capacity ofthe system is derived. It is shown that an array power gainof O(pM) is achievable. It is also observed that phase noiseeffectively limits the fraction of the time used for informationtransmission and the number of users in the system. Finally itis concluded that, phase noise degrades the performance butdoes not eliminate the fundamental gains of a Large ScaleAntenna System (LSAS), i.e., power efficiency and high sumrate performance with low complexity receiver processing.

• 348.
On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems2012Ingår i: IEEE Wireless Communications Letters, ISSN 2162-2337, E-ISSN 2162-2345, Vol. 1, nr 4, s. 276-279Artikel i tidskrift (Övrigt vetenskapligt)

A single carrier transmission scheme is presentedfor the frequency selective multi-user (MU) multiple-input singleoutput(MISO) Gaussian Broadcast Channel (GBC) with a basestation (BS) having M antennas and K single antenna users.The proposed transmission scheme has low complexity andfor M ≫ K it is shown to achieve near optimal sum-rateperformance at low transmit power to receiver noise power ratio.Additionally, the proposed transmission scheme results in anequalization-free receiver and does not require any MU resourceallocation and associated control signaling overhead. Also, thesum-rate achieved by the proposed transmission scheme is shownto be independent of the channel power delay profile (PDP). Interms of power efficiency, the proposed transmission scheme alsoexhibits an O(M) array power gain. Simulations are used toconfirm analytical observations.

• 349.
Uplink Performance of Time-Reversal MRC in Massive MIMO Systems subject to Phase Noise2015Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 14, s. 711-723Artikel i tidskrift (Refereegranskat)

Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an excess of base station (BS) antennas (Massive MIMO) offer unprecedented multiplexing gains and radiated energy efficiency. Oscillator phase noise is introduced in the transmitter and receiver radio frequency chains and severely degrades the performance of communication systems. We study the effect of oscillator phase noise in frequency-selective Massive MIMO systems with imperfect channel state information (CSI) and M BS antennas. In particular, we consider two distinct operation modes, namely when the phase noise processes at the BS antennas are identical (synchronous operation) and when they are independent (non-synchronous operation). We analyze a linear and low-complexity time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both operation modes we derive a lower bound on the sum-capacity and we compare the performance of the two modes. Based on the derived achievable sum-rate, we show that with the proposed receive processing an O($\sqrt{M}$) array gain is achievable. Due to the phase noise drift the estimated effective channel becomes progressively outdated. Therefore, phase noise effectively limits the length of the interval used for data transmission and the number of scheduled users. The derived achievable rates provide insights into the optimum choice of the data interval length and the number of scheduled users.

• 350.
University of Pisa, Italy.
Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten. University of Pisa, Italy. Linköpings universitet, Institutionen för systemteknik, Kommunikationssystem. Linköpings universitet, Tekniska fakulteten.
Network Deployment for Maximal Energy Efficiency in Uplink with Multislope Path Loss2018Ingår i: IEEE Transactions on Green Communications and Networking, E-ISSN 2473-2400, Vol. 2, nr 3, s. 735-750Artikel i tidskrift (Refereegranskat)

This work aims to design the uplink (UL) of a cellular network for maximal energy efficiency (EE). Each base station (BS) is randomly deployed within a given area and is equipped with M antennas to serve K user equipments (UEs). A multislope (distance-dependent) path loss model is considered and linear processing is used, under the assumption that channel state information is acquired by using pilot sequences (reused across the network). Within this setting, a lower bound on the UL spectral efficiency and a realistic circuit power consumption model are used to evaluate the network EE. Numerical results are first used to compute the optimal BS density and pilot reuse factor for a Massive MIMO network with three different detection schemes, namely, maximum ratio combining, zero-forcing (ZF) and multicell minimum mean-squared error. The numerical analysis shows that the EE is a unimodal function of BS density and achieves its maximum for a relatively small density of BS, irrespective of the employed detection scheme. This is in contrast to the single-slope (distance-independent) path loss model, for which the EE is a monotonic non-decreasing function of BS density. Then, we concentrate on ZF and use stochastic geometry to compute a new lower bound on the spectral efficiency, which is then used to optimize, for a given BS density, the pilot reuse factor, number of BS antennas and UEs. Closed-form expressions are computed from which valuable insights into the interplay between optimization variables, hardware characteristics, and propagation environment are obtained.

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